1. Field of the Invention
The present invention relates to the switching of space and time division multiplexed transmissions and more particularly, to a novel switching element and novel network configuration for implementing a substantially continuously expandable switching network in a telephone exchange, telephone central office, PABX, remote concentrator, data circuit switch or other device wherein a plurality of terminal interconnections are required.
2. Description of the Prior Art
Presently available time division switching networks utilize time-slot-interchange modules or space switching modules utilizing time shared space interconnections, usually two of the former modules and one of the latter or two of the latter modules and one of the former. U.S. Pat. No. 3,770,895 is illustrative of a time slot interchange of the prior art. U.S. Pat. No. 3,963,872 is illustrative of a folded multiple stage switching network of the prior art. These known prior art switching networks are incapable of unlimited growth without extensive recabling to accommodate major system size expansion.
Switching networks of the prior art are designed to cover particular size ranges, i.e., the number of lines that can be switched, whereas the present invention is adaptable to switch over a wide and expandable size range.
In accordance with the present invention, a small switching network, i.e., for a few hundred lines, may be economically constructed using only the minimum number of stages required for implementing such a small network. There is no upper limit from a network configuration standpoint to the expandability of such a small network, i.e., the network is readily expandable from a few hundred lines requiring a small number of stages to a large number of lines, i.e., 50,000 lines, requiring a plurality of stages. Also, a working small network can be readily expanded to a large working network without recabling as would be required in systems of the prior art.
A continuously expandable switching network configuration is described wherein the outlets of the stages comprising the network are connected only to the switches in higher level stages, thereby eliminating the need for recabling in the event of system expansion. The connections between terminals are accomplished by use of the reflection and the connection characteristics of the individual switching elements. By reflection characteristics, the capability of interconnecting two inlets within the switch is defined. This network is implementable with either analog or digital transmission schemes over either two or four wire traffic paths and with space and time switching and combinations thereof. In a preferred embodiment of this invention, a combined multistage space switch and time slot interchange switching network is described utilizing as individual switching elements thereof an integrated signal switch and control circuit by which traffic can be interconnected to another inlet or connected to an outlet. The described network configuration is applicable to either analog or digital traffic switching and is advantageous when employed in a four wire network as either a group switch, a concentrator, a deconcentrator or any other type of PCM switching unit requiring the capability of space and time switching to connect any time slot on any incoming multiplexed line to any other time slot on any other outgoing multiplexed line. The described switch may be incorporated in the network for switching both the forward and return paths of four wire interconnections by means of a controllable reflection point technique and a path selection control by means of control signals transmitted over the speech path to be controlled thereby eliminating extra control lines. Of course, if desired, such control signals could be transmitted over separate control wires. It is therefore a primary object of the present invention to provide a substantially continuously expandable switching network.
A further object of the present invention is to provide an expandable switching network in which modification of internal or external connecting links is not required for such expansion.
A further object of the present invention is to provide a multistage switching network in which the switching element outlets of any stage are connected to switching element inlets of higher order stages.
Yet another object of the present invention is to provide a multistage switching network in which incoming traffic penetrates the network to the extent necessary to complete required connections.
Yet another object of the present invention is to provide a switching element having a plurality of inlets connectable to a plurality of outlets, having a reflection capability of reflecting traffic entering on any inlet back to any other inlet, and a connection capability of connecting any inlet to any outlet.
Yet another object of the present invention is to provide a PCM (pulse code modulated) switch module which allows continuously expandable networks without recabling over a size range, i.e., the total number of terminals to be interconnected, of 100:1 or more and which is implementable as a group switch, a concentrator or a deconcentrator. Pulse code modulation is a type of pulse modulation wherein the modulating signal waveform is sampled at regular intervals, quantized into discrete steps and digitally coded into a series of pulses.
Yet another object of the present invention is to provide a PCM switch for connecting any time slot on any multiplexed line to any other time slot on any other multiplexed line.
Yet another object of the present invention is to provide a combined space and time switching module for switching both the forward and return paths of a four wire connection.
Yet another object of the present invention is to provide a combined time and space switch module having a path selection control accessible for control commands by means of the voice path with the consequent elimination of extraneous control paths.
The foregoing and other features and advantages of the invention will be apparent from the following more detailed description of the preferred embodiments of the invention as illustrated by the accompanying drawings.